In commonly assigned U.S. Pat. No. 4,788,439, issued Nov. 29, 1988, entitled "Multiple Detector Fog Suppression and Edge Enhancement" A. H. Hardy et al. describe a proximity sensing system that detects target objects while protecting against false target detection due to fog, clouds, or other aerosols. One or more target detectors are alternately disposed adjacent to one or more guard detectors in such a manner that the edges of fields of view are immediately adjacent. Positive signals generated from target detectors are summed with negative signals from the guard detectors. The summing action steepens the slope of the summed signal that is produced when a target image moves onto the edge of a target detector.
In U.S. Pat. No 4,479,053, issued Oct. 23, 1984, entitled "Focal Plane Array Optical Proximity Sensor" A. R. Johnson discloses an optical proximity sensor that includes an illuminator assembly and a detector assembly. Lenses associated with each assembly are spaced apart in order to define a predetermined detection volume.
One problem associated with some target detection systems of the prior art is that an excessive sensitivity is experienced for objects located within a predetermined distance range. This excessive sensitivity results from optical side lobes and multiple reflections.
It is therefore an object of the invention to provide for a substantial elimination of excessive response within a predetermined range of a receiver element associated with a target detector system.